An amount of information stored and used by people and electronic equipment has been steadily increasing with development of information and network technology based on digitization. In order to build a secure and safe community for a human society which has been distracted by a large amount of information, it is important for people to acknowledge useful information by acquiring accurate data of events from a sensor which serves as an input device, and analyzing, determining and processing the data.
In modern life, facilities such as water and sewage networks, high pressure chemical pipelines for gas, oil, and the like, high speed railways, long-span bridges, high-rise buildings, large passenger aircrafts, and automobiles have been built and have become a basis of a rich social infrastructure. If destruction be associated with natural disasters such as unexpected earthquakes and deterioration of lifetimes lead to a serious accident, impacts on society will be enormous, and economic losses will be large. Deterioration such as corrosion, wear and rattling of members used in the facilities will worsen as a time of use elapses, which will eventually lead to malfunction such as destruction. In order to ensure reassurance and safety of the facilities, great efforts have been made in technology developments beyond academic areas such as science, engineering, and sociology. Among these, development of a non-destructive inspection technique which is a low cost and simple-to-operate inspection technique has become increasingly important in achieving prevention of serious accidents due to deterioration or destruction of the facilities.
Various methods for non-destructive inspection techniques for water leak in water and sewage networks, gas leak in gas pipes, and leak in various pipes in chemical plants have been proposed and have been put to practical use. An inspection method using a vibration sensor has been known as a typical conventional non-destructive inspection method. In this inspection method, a vibration sensor is arranged on a pipe, a place in contact with a pipe, for example, a ground surface adjacent to where the pipe is buried, and the like and vibration caused by a leak of the pipe is detected.
Furthermore, PTL 1 discloses a technology in which leak detection accuracy is improved by removing extraneous vibration superimposed on vibration caused by a leak. The extraneous vibration includes passing sounds of transportation means such as automobiles and trains, natural sounds of the atmosphere such as wind, and extraneous noises such as human voices. In PTL 1, two detectors consisting of a vibration detector for detecting leak vibration and extraneous vibration and a vibration detector for detecting only extraneous vibration are provided, and leak detection accuracy is improved by means of generating only vibration due to a leak by removing extraneous vibration by obtaining a difference of signals from the two detectors.